Key Points

Insolation is the incoming solar radiation received by the Earth's surface, primarily in the form of short wavelengths. It is the main source of energy for almost all processes on Earth.

Perihelion is when the Earth is nearest to the sun (around January 3rd), receiving slightly more insolation. Aphelion is when it is farthest from the sun (around July 4th), receiving slightly less insolation.

The amount of insolation varies due to factors like the Earth's rotation, the angle of the sun's rays based on latitude, the length of the day, and the transparency of the atmosphere.

At higher latitudes, the sun's rays are slanted, spreading energy over a larger area and passing through more atmosphere, which reduces the intensity of insolation received per unit area.

Insolation is highest in subtropical deserts due to low cloudiness, and lowest at the poles. The equator receives comparatively less insolation than the tropics because of frequent cloud cover.

The atmosphere is heated by conduction (direct contact with Earth), convection (vertical air movement), and advection (horizontal air movement or wind). Advection is crucial for most daily weather variations.

The Earth, after being heated by short-wave insolation, radiates heat back into the atmosphere in the form of long-wave radiation. This process, known as terrestrial radiation, heats the atmosphere from below.

The Earth maintains a stable temperature because the amount of incoming solar radiation is balanced by the amount of outgoing terrestrial radiation. This is known as the heat budget or heat balance of the Earth.

Albedo is the percentage of solar radiation reflected back to space by a surface. About 35 percent of incoming radiation is reflected by clouds, ice, snow, and the Earth's surface before it is absorbed.

There is a net radiation surplus in the tropics (between 40 degrees North and South) and a deficit at the poles. This imbalance drives the global circulation of atmosphere and oceans, transferring heat from the tropics towards the poles.

The main factors influencing temperature at any place are latitude, altitude, distance from the sea, air-mass circulation, and the presence of warm or cold ocean currents.

The Normal Lapse Rate is the rate at which temperature decreases with an increase in altitude. On average, the temperature drops by 6.5 degrees Celsius for every 1,000 meters of ascent.

Land heats up and cools down faster than water. Therefore, coastal areas experience a moderate climate with a lower temperature range compared to continental interiors.

Isotherms are lines on a map that connect places having the same temperature. They are used to show the global distribution of temperature, which generally follows the parallels of latitude.

In the Northern Hemisphere's winter (January), isotherms bend south over continents (colder) and north over oceans (warmer). The Southern Hemisphere has more regular isotherms due to its large ocean area.

Temperature inversion is a condition where the normal lapse rate is reversed, and temperature increases with altitude. This often occurs on long, clear winter nights and can trap pollutants and cause fog.